ISO/FDIS 20138-1

ISO/TC 269/SC 02/WG 1 2
Secretariat: AFNOR
Date: 2025-09-10
Railway applications — Calculation of braking performance
(stopping, slowing and stationary braking) — Part 1: General
algorithms utilizing mean value calculation —
Second edition
Date: 2025-06-17
ISO #####-#:####(X)
Part 1:
General algorithms utilizing mean value calculation
Applications ferroviaires — Calcul des performances de freinage (freinage d'arrêt, de ralentissement et
d'immobilisation) —
Partie 1: Algorithmes généraux utilisant le calcul par la valeur moyenne
FDIS stage
2 © ISO #### – All rights reserved

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO'sISO’s member body in the country of the requester.
ISO Copyright Office copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
iii
Contents
Foreword . v
Introduction . vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Stopping and slowing distances calculation . 8
5.1 General. 8
5.2 Rail vehicle characteristics . 10
5.3 Wheel/rail adhesion dependent brake unit type characteristics . 11
5.4 Wheel/rail adhesion independent brake unit characteristics . 22
5.5 Time characteristics . 26
5.6 Initial and operating characteristics . 28
5.7 Stopping and slowing distance calculation based on mean values. 32
5.8 Additional dynamic calculations . 34
6 Stationary braking . 35
6.1 General. 35
6.2 Holding brake . 35
6.3 Immobilization brake . 35
6.4 Parking brake . 35
6.5 Stationary brake calculation . 35
6.6 Static coefficient of friction . 36
6.7 Parking brake application force provided by the different subsystems . 36
6.8 Retention force of an individual wheelset, 𝑭st,ax,(𝒊, 𝝉a). 43
6.9 Total retention force per train, 𝑭st(𝒊, 𝝉a) . 43
6.10 Stationary brake safety calculation . 43
6.11 Safety ratio for stationary brake (retention safety), 𝑺st(𝒊, 𝝉a) . 45
6.12 Static coefficient of wheel/rail adhesion required by each disc braked wheelset, τreq,st,ax 45
6.13 Coefficient of wheel/rail adhesion required by each wheelset with block brake or tread
brake. 45
6.14 Maximum achievable gradient, imax . 46
6.15 Additional results for stationary brake calculation for rail vehicle or unit . 46
Annex A (informative) Methodology of stopping and slowing distance calculation . 48
Annex B (informative) Workflow for stationary brake calculations . 51
Annex C (informative) Examples for brake calculation . 54
Annex D (informative) Calculation of braking or retarding forces (non-stationary) . 71
Annex E (informative) Additional results for stationary brake calculation for rail vehicle or unit
with a different relationship between braking force and load per wheelset . 77
Annex F (informative) Tread brake with different lever length ratios . 90
Bibliography . 91

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 269, Railway applications, Subcommittee SC 2,
Rolling stock.
This second edition cancels and replaces the first edition (ISO 20138-1:2018), which has been technically
revised.
The main changes are as follows:
— — a normative reference to ISO 24478 has been added to Clause 2;
— — new terms “brake subsystem” and “mean swept radius” have been added to 3Clause 3;;
— 4— Clause 4 “Symbols"” with Table 1Table 1 have been revised;
— — the symbols that are explained in Table 1Table 1 have been deleted infrom formulae keys;
— 5— Clause 5 “Stopping and slowing distances calculation” has been revised;
— 6— Clause 6 “Stationary braking” has been revised;
— Annex A— Annex A “Methodology of stopping and slowing distance calculation” has been revised;
— Annex B— Annex B “Workflow for stationary brake calculations” has been revised;
— Annex C— Annex C “Examples for brake calculation” has been revised;
— Annex D— Annex D “Calculation of braking forces (non-stationary)” has been revised;
v
— Annex E— Annex E “Additional results for stationary brake calculation for rail vehicle or unit with a
different relationship between braking force and load per wheelset“ and Annex FAnnex F “Tread brake
with different lever length ratios” have been added;
— — the Bibliography has been revised.
A list of all parts in the ISO 20138 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
vi
Introduction
The objective of this document is to enable the railway industry and operators to work with common
calculation methods.
This document (i.e. ISO 20138--1) and the second part (ISO 20138--2) complement each other but also can be
used separately, depending on the requirements of the user.
— — In this document, the braking force equals the retarding force, as the assumed braking forces used in
a brake calculation never exceed the values which can be transferred by the assumed wheel/rail adhesion.
— — ISO 20138--2 details the step by step calculation methodology utilizing instantaneous values of
braking force provided by each operational brake system throughout the stopping or slowing time.
vii
Railway applications — Calculation of braking performance
(stopping, slowing and stationary braking) — —
Part 1:
General algorithms utilizing mean value calculation
1 Scope
This document specifies the methodologies for the calculation of braking performance for railway rolling
stock.
This document describes the general algorithms and formulae using mean value inputs to perform the
calculations of braking performance in terms of stopping and slowing distances, stationary braking, and power
and energy for all types of rolling stock, either as single rail vehicles or train formations, with respect to the
braking distance.
The calculations can be used at any stage of the development and assessment process (design, manufacturing,
testing, verification, investigation, etc.) of railway rolling stock.
This document does not set out specific acceptance criteria (pass or fail). This document is not intended to be
used as a design guide for the selection of brake systems. This document does not specify performance
requirements.
This document contains examples of the calculation of braking forces for different brake systems and
calculation of stopping distance and stationary braking relevant to a single rail vehicle or a train. This
document does not provide a method to calculate the extension of stopping distances when the level of
available wheel/rail adhesion is exceeded (wheel slide activity).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 20138-2:2025, Railway applications — Calculation of braking performance (stopping, slowing and
stationary braking) — Part 2: General algorithms utilizing step by step calculation
ISO 22575, Railway applications —General terms and definitions
ISO 24478:2023, Railway applications — Braking — General vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 24478, ISO 22575 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
train
formation consisting of one or more units capable for self-propelled operation
[SOURCE: ISO 22575:2025, 3.4]
3.2 3.2
trainset
fixed formation(s) that
...